Search NASA⌕ Search

SEARCH · Search NASA

Results for “substrate amorphization”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

Ion beam deposition of amorphous carbon films with diamond like properties

Carbon films were deposited on silicon, quartz, and potassium bromide substrates from an ion beam. Growth rates were approximately 0.3 micron/hour. The films were featureless and amorphous and contained only carbon and hydrogen in significant amounts. The density and carbon/hydrogen ratio indicate the film is a hydrogen deficient polymer. One possible structure, consistent with the data, is a random network of methylene linkages and tetrahedrally coordinated carbon atoms.

Angus, John C.↗
DOE OSTI2021

Phase‐Change‐Memory Process at the Limit: A Proposal for Utilizing Monolayer Sb 2 Te 3

Abstract One central task of developing nonvolatile phase change memory (PCM) is to improve its scalability for high‐density data integration. In this work, by first‐principles molecular dynamics, to date the thinnest PCM material possible (0.8 nm), namely, a monolayer Sb 2 Te 3 , is proposed. Importantly, its SET (crystallization) process is a fast one‐step transition from amorphous to hexagonal phase without the usual intermediate cubic phase. An increased spatial localization of electrons due to geometrical confinement is found to be beneficial for keeping the data nonvolatile in the amorphous phase at the 2D limit. The substrate and superstrate can be utilized to control the phase change behavior: e.g., with passivated SiO 2 (001) surfaces or hexagonal Boron Nitride, the monolayer Sb 2 Te 3 can reach SET recrystallization in 0.54 ns or even as fast as 0.12 ns, but with unpassivated SiO 2 (001), this would not be possible. Besides, working with small volume PCM materials is also a natural way to lower power consumption. Therefore, the proposed PCM working process at the 2D limit will be an important potential strategy of scaling the current PCM materials for ultrahigh‐density data storage.

2D limit↗
DOE OSTI2020

Radiation response of FeCrAl-coated Zircaloy-4

Coating the surface of Zircaloy-4 light water reactor fuel cladding tube is of considerable interest for enhancing its accident tolerance. In this study, thermal annealing of FeCrAl-coated Zircaloy-4 at 725 °C for 500 h, was used to induce interfacial reactions between Zircaloy-4 and FeCrAl. The interface zones were then irradiated by 3.5 MeV Zr ions at 400 °C, up to 50, 100, 150 peak dpa values. Transmission electron microscopy (TEM) and scanning TEM were used to characterize microstructural and composition changes before and after ion irradiation. Three interfacial phases were identified: FeZr 3 , (Fe,Cr) 2 Zr, and ZrC. The widest intermetallic layer, FeZr3, had large grains. The narrower phases, (Fe,Cr)2Zr and ZrC, contained small grains and were often mixed. The unexpected observation of the ZrC phase was attributed to the presence of very small impurity level concentrations of carbon in the powder material. No void swelling was observed in any of the phases, including the FeCrAl coating and Zircaloy-4 substrate. (Fe,Cr) 2 Zr, however, fully amorphized after irradiation, even at the lowest dpa.

36 MATERIALS SCIENCE↗
NASA NTRS1984

Coaxial carbon plasma gun deposition of amorphous carbon films

A unique plasma gun employing coaxial carbon electrodes was used in an attempt to deposit thin films of amorphous diamond-like carbon. A number of different structural, compositional, and electrical characterization techniques were used to characterize these films. These included scanning electron microscopy, scanning transmission electron microscopy, X ray diffraction and absorption, spectrographic analysis, energy dispersive spectroscopy, and selected area electron diffraction. Optical absorption and electrical resistivity measurements were also performed. The films were determined to be primarily amorphous, with poor adhesion to fused silica substrates. Many inclusions of particulates were found to be present as well. Analysis of these particulates revealed the presence of trace impurities, such as Fe and Cu, which were also found in the graphite electrode material. The electrodes were the source of these impurities. No evidence of diamond-like crystallite structure was found in any of the film samples. Details of the apparatus, experimental procedure, and film characteristics are presented.

Sater, D. M.↗
NASA NTRS1990

Future mission opportunities and requirements for advanced space photovoltaic energy conversion technology

The variety of potential future missions under consideration by NASA will impose a broad range of requirements on space solar arrays, and mandates the development of new solar cells which can offer a wide range of capabilities to mission planners. Major advances in performance have recently been achieved at several laboratories in a variety of solar cell types. Many of those recent advances are reviewed, the areas are examined where possible improvements are yet to be made, and the requirements are discussed that must be met by advanced solar cell if they are to be used in space. The solar cells of interest include single and multiple junction cells which are fabricated from single crystal, polycrystalline and amorphous materials. Single crystal cells on foreign substrates, thin film single crystal cells on superstrates, and multiple junction cells which are either mechanically stacked, monolithically grown, or hybrid structures incorporating both techniques are discussed. Advanced concentrator array technology for space applications is described, and the status of thin film, flexible solar array blanket technology is reported.

Flood, Dennis J.↗
NASA NTRS2005

Low-cycle Fatigue and Dynamic Fracture in Gold Thin Films on SiN Supported Membranes

This slide presentation focuses on the dynamic mechanical response and fatigue behavior in sub-micron thick Au-films deposited onto amorphous Si(sub X)N(sub y) substrates, with spider-web geometry, that were subjected to forced vibration (3-axis random vibration with 2 kHz roll-off frequency). The work is to advance cyrogenic detectors that can operate at 100mK, that is required to create cryogenic detectors that are to search for present day signatures of the big bang.

fatigue↗
DOE OSTI2025

Plasma Flow Reactor Investigation into Nucleation of Uranium Oxide on Silica Substrates to Better Understand Fallout Formation

Understanding particulate formation in nuclear debris is critical for predicting fallout transport after a nuclear event. Improved characterization of fallout formation and transport could lead to better guidance for emergency response in a post-detonation scenario. By analyzing how U-oxides nucleate onto different forms of SiO 2 (crystalline and amorphous), we can gain insight into how entrained environmental materials may incorporate into fallout. In this experiment a Plasma Flow Reactor (PFR), was used to replicate the high temperature and extreme flow conditions in a nuclear fireball. Uranyl nitrate was injected into the plasma, and PFR-generated Uranium oxides were allowed to condense onto amorphous (nanoparticles of varying sizes) or crystalline (quartz) SiO 2 substrates. SiO 2 substrates were characterized before and after U-oxide deposition using Scanning Electron Microscopy (SEM) based techniques (i.e. EDS) in order to characterize how U-oxides may nucleate onto these substrates. After a collection time of 4 minutes at an RF coil distance of 25cm, both the amorphous SiO 2 nanoparticles and the crystalline structures demonstrated dendritic nucleation of U-oxide species as identified by SEM/EDS.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2022

Effect of substrate temperature on sputter-deposited boron carbide films

Sputter deposition of B4C films with tailored physical properties remains a challenge. Here, we systematically study how substrate temperature influences the properties of B4C films deposited by direct current magnetron sputtering onto planar substrates held at temperatures in the range of 100-510°C. Results show that all films are amorphous stoichiometric B4C, with low O content of ~1 at. %. Films deposited onto substrates at 100°C exhibit high compressive residual stress and decreased mechanical properties. Therefore, for elevated substrate temperatures in the range of 180-510°C, film mass density, surface roughness, Young’s modulus, and hardness are weakly dependent on substrate temperature. However, in this temperature range, an increase in substrate temperature leads to larger residual compressive stress accompanied by a corresponding reduction in the concentration of nanoscale inhomogeneities. At least for the landing atom ballistics conditions studied here, a substrate temperature range of ~185-250°C is optimum for growing films with near-zero intrinsic residual stress. The overall weak substrate temperature dependence of film properties revealed in this work is favorable for the development of a robust deposition process, particularly for the case of deposition onto non-planar substrates where temperature control is often challenging.

36 MATERIALS SCIENCE↗
DOE OSTI2022

A molecular dynamics survey study of impact-induced amorphization in yttria nanoparticles

The impact of a single yttria (Y 2 O 3 ) nanoparticle onto a yttria substrate was studied as a function of particle velocity (300–1200 m/s) and diameter (5–12 nm) for three particle orientations and two substrate orientations using molecular dynamics simulations. Impacts resulted in minimal dislocation motion but extensive disordering of the crystal lattice without approaching the melting temperature. The resulting amorphous microstructure was both precisely coincident with plastic strain and retained until the end of the simulation, suggesting a deformation mechanism of amorphization-facilitated viscous flow. Further analysis revealed that the degree of amorphization depended primarily on the impact velocity and secondarily on the orientations of the particle and substrate, with significant second-order effects from variable interactions.

74 ATOMIC AND MOLECULAR PHYSICS↗
NASA NTRS1976

Solid-state growth of Si to produce planar surfaces

Paralleling the sophisticated control of Si and GaAs growth from fluid media, we demonstrate control of Si growth using a solid growth medium. Faceted dissolution pits were first produced in a Si substrate using standard photolithographic techniques and Al metallization. Si was then evaporated onto the cold structure, depositing as amorphous material. Upon heating, the amorphous Si migrated through the solid Al and grew rapidly in the faceted pits, typically refilling them flush with the surrounding substrate. Evidence that the rapid growth occurs only while the amorphous Si is dissolving into the Al is presented.

Boatright, R. L.↗
DOE OSTI2021

Compositional and phase dependence of elastic modulus of crystalline and amorphous Hf 1- x Zr x O 2 thin films

The elastic moduli of amorphous and crystalline atomic layer-deposited Hf 1-x Zr x O 2 (HZO, x = 0, 0.31, 0.46, 0.79, 1) films prepared with TaN electrodes on silicon substrates were investigated using picosecond acoustic measurements. The moduli of the amorphous films were observed to increase between 211 ± 6 GPa for pure HfO 2 and 302 ± 9 GPa for pure ZrO 2 . In the crystalline films, it was found that the moduli increased upon increasing the zirconium composition from 248 ± 6 GPa for monoclinic HfO 2 to 267 ± 9 GPa for tetragonal ZrO 2 . Positive deviations from this increase were observed for the Hf 0.69 Zr 0.31 O 2 and Hf 0.54 Zr 0.46 O 2 compositions, which were measured to have moduli of 264 ± 8 GPa and 274 ± 8 GPa, respectively. These two compositions contained the largest fractions of the ferroelectric orthorhombic phase, as assessed from polarization and diffraction data. The biaxial stress states of the crystalline films were characterized through sin 2 (ψ) x-ray diffraction analysis. The in-plane stresses were all found to be tensile and observed to increase with the increasing zirconium composition, between 2.54 ± 0.6 GPa for pure HfO 2 and 5.22 ± 0.5 GPa for pure ZrO 2 . The stresses are consistent with large thermal expansion mismatches between the HZO films and silicon substrates. Furthermore, these results demonstrate a device-scale means to quantify biaxial stress for investigation on its effect on the ferroelectric properties of hafnia-based materials.

36 MATERIALS SCIENCE↗
NASA NTRS1995

Probing the structure of cometary ice

Computer simulations of bulk and vapor deposited amorphous ices are presented. The structure of the bulk low density amorphous ice is in good agreement with experiments on pressure disordered amorphous ice. Both the low density bulk ice and the vapor deposited ices exhibit strong ordering. Vapor deposition of hot (300 K) water molecules onto a cold (77 K) substrate yields less porous ices than deposition of cold (77 K) water molecules onto a cold substrate. Both vapor deposited ices are more porous than the bulk amorphous ice. The structure of bulk high density amorphous ice is only in fair agreement with experimental results. Attempts to simulate high density amorphous ice via vapor deposition were not successful. Electron diffraction results on vapor deposited amorphous ice indicate that the temperature of the nucleation of the cubic phase depends upon the amount of time between the deposition and the onset of crystallization, suggesting that freshly deposited ice layers reconstruct on time of the order of hours. The temperature dependence of the microporosity of the vapor deposited amorphous ices might affect laboratory experiments that are aimed at simulating astrophysical ices in the context of the origin of prebiotic organic material and its transport to the Earth.

Wilson, Michael A.↗
DOE OSTI2026

Epitaxial registry and transport properties in V4O7 thin films

We report the growth of V4O7 thin films deposited simultaneously on amorphous SiO2 and crystalline c-cut Al2O3 substrates. x-ray diffraction shows that films grown on SiO2 are polycrystalline with no preferred orientation, while films grown on Al2O3 exhibit a well-defined out-of-plane orientation and an in-plane registry consistent with epitaxial growth. Transmission electron microscopy confirms the crystallographic relationship between the V4O7 film and the Al2O3 substrate. Atomic force microscopy indicates substantially lower surface roughness for films grown on Al2O3 (~6 nm) compared to those grown on SiO2 (~22 nm), and Raman spectroscopy confirms stabilization of the same V4O7 phase on both substrates. Electrical transport measurements reveal a metal–insulator transition near 244 K for both substrates, with thermal hysteresis not exceeding ~1 K. Although the transition temperature remains essentially unchanged, films grown on Al2O3 exhibit higher conductivity over the entire temperature range, exceeding that of films grown on SiO2 by approximately two orders of magnitude at 100 K and by a factor of five at 300 K. These results indicate that the conductivity differences are consistent with variations in microstructural connectivity associated with crystallographic order.

36 MATERIALS SCIENCE↗
NASA NTRS1972

Optical polarimetric properties of the Echo 2 and PAGEOS 1 engineering surfaces

Experimental investigations of the percent polarization of sunlight reflected from the surfaces of each of the Echo 2 Satellite and PAGEOS (Passive Geodetic Earth Orbiting Satellite) were performed to determine the stability of their surfaces in the space environment. The Echo 2 surface material was amorphous phosphate chemically bonded to a rolled aluminum substrate while the PAGEOS 1 surface material is vapor deposited aluminum on a poly (ethylene terephthalate) film. The stability of the satellites' surfaces was analyzed by comparing the light polarizing properties of the satellites, to those of test surfaces representative of the satellites' surfaces. The properties of flat test surfaces were measured experimentally in the laboratory, and the effects of surface strain, surface geometry, and vacuum upon these properties were examined. The laboratory analyses revealed that the polarization properties of the Echo 2 surface were significantly affected by surface geometry and vacuum, and that the properties of the PAGEOS 1 surface were not significantly altered by any of the above mechanisms.

Lee, R. B., III↗
NASA NTRS1990

Optical constants of solid methane

Methane is the most abundant simple organic molecule in the outer solar system bodies. In addition to being a gaseous constituent of the atmospheres of the Jovian planets and Titan, it is present in the solid form as a constituent of icy surfaces such as those of Triton and Pluto, and as cloud condensate in the atmospheres of Titan, Uranus, and Neptune. It is expected in the liquid form as a constituent of the ocean of Titan. Cometary ices also contain solid methane. The optical constants for both solid and liquid phases of CH4 for a wide temperature range are needed for radiative transfer calculations, for studies of reflection from surfaces, and for modeling of emission in the far infrared and microwave regions. The astronomically important visual to near infrared measurements of solid methane optical constants are conspicuously absent from the literature. Preliminary results are presented on the optical constants of solid methane for the 0.4 to 2.6 micrometer region. Deposition onto a substrate at 10 K produces glassy (semi-amorphous) material. Annealing this material at approximately 33 K for approximately 1 hour results in a crystalline material as seen by sharper, more structured bands and negligible background extinction due to scattering. The constant k is reported for both the amorphous and the crystalline (annealed) states. Typical values (at absorption maxima) are in the .001 to .0001 range. Below lambda = 1.1 micrometers the bands are too weak to be detected by transmission through the films less than or equal to 215 micrometers in thickness, employed in the studies to date. Using previously measured values of the real part of the refractive index, n, of liquid methane at 110 K, n is computed for solid methane using the Lorentz-Lorenz relationship. Work is in progress to extend the measurements of optical constants n and k for liquid and solid to both shorter and longer wavelengths, eventually providing a complete optical constants database for condensed CH4.

Khare, Bishun N.↗
DOE OSTI2025

Effects of substrate bias and tilt on magnetron sputtered boron carbide films

Maintaining high density and good mechanical properties at oblique angles for magnetron sputtered amorphous boron carbide films remains a challenge. In this study, we investigate the effect of the substrate bias on density, residual stress, mechanical properties, and morphology of boron carbide films deposited via direct current magnetron sputtering with a full-face erosion magnetron source in a mixed Ar-Ne plasma. Results show that films deposited at oblique substrate tilt angles on substrates biased at -50 V possess significantly lower oxygen content, superior mechanical properties, and higher density compared to their electrically grounded counterparts. In conclusion, these enhancements observed at oblique angles, while promising, come at the cost of larger residual compressive stress and higher Ne incorporation in films.

Materials science↗